There are 50 million reasons why they play Ruiz too much, not one has to do with talent.
I'm not sure the argument that he plays because of his contract holds weight anymore. This team has been quick to ditch poor performers despite contracts this year (Lopez, Poche, Sims, to name a few).
IMHO, Ruiz plays because there's nobody better, and because he's still young and the team is hopeful he'll improve.